The present invention relates to highly efficient marine propulsion systems, which are not based on conventional water-screw technology. In particular, the present invention relates to using magnetohydrodynamic technology for propulsion in marine vessels.
Due to the cavitation limits of water-screw (i.e., propeller) technology, highly efficient propulsion mechanisms which are not based on water-screw technology are needed to maximize the speed of marine vessels (i.e., vessels that are propelled in the water and under the surface of water, for example, boats, submarines, torpedoes, or underwater missiles). Three technologies, magnetohydrodynamic (xe2x80x9cMHDxe2x80x9d) propulsion, the analog of airborne rocket propulsion, and ram-jet technology, have been proposed for this purpose. All three technologies offer the potential for exceeding the speed of conventional propeller-based vessels. These technologies are not subject to the cavitation limits of water-screw technology and they minimize the number of moving parts in contact with the water stream.
The latter two technologies are mechanical propulsion systems. A simple (xe2x80x9clow-techxe2x80x9d) version of the first, jet propulsion, is described in U.S. Pat. No. 5,267,883 to Gudmundsen, issued Dec. 7, 1993, as not involving the mechanical compression of water containers. This technology is appropriate for surface marine vehicles because it uses a cyclic vacuum pump to draw water from the environment and then expel it like a jet. An example of the second system, ram-jet technology, described in U.S. Pat. No. 5,598,700 to Varshay et al., issued Feb. 4, 1997, involves underwater propulsion by inserting a gaseous jet stream into the water flow to obtain a water ram-jet operation. The gaseous jet stream is assumed to be derived from a separate energy source such as solid rocket fuel.
Although both of these exemplary methods are operable, they are significantly inefficient in converting stored energy into kinetic energy. Gudmundsen""s method uses an external energy source to mechanically power a vacuum pumping system which then transforms the pressure differential into kinetic energy of the water stream. Varshay et al.""s system may have fewer moving parts, but the energy still undergoes conversion into a gaseous jet, which suffers significant friction loss at the jet injectors. Furthermore, the efficiency of the ram-jet operation depends on the efficiency of the heat exchange between the gaseous jet and the water. These multiple conversions of energy reduce the final usable kinetic energy.
An alternative to these technologies is MHD propulsion, which uses the natural electrical conductivity of sea water as a power source. The advantages of MHD are quiet operation due to the absence of moving parts, high speed due to the absence of a cavitation limit, and high efficiency due to the nearly direct conversion of electrical energy into kinetic energy. Furthermore, the maximum theoretical efficiencies are relatively well understood. O. M. Phillips""s early prediction (in xe2x80x9cThe Prospects for Magnetohydrodynamic Ship Propulsion,xe2x80x9d Journal of Ship Research, pp. 43-51 (March 1962)) that top speeds on the order of 10 knots would be the limit for 600-foot vessels, was finally met with the 1992 commercial launch of the Yamato-I, a 30 m, 280 ton catamaran. In addition, D. Choi et al. (in xe2x80x9cApplication of Scalar Implicit Approximate Factorization for Underwater Magnetohydrodynamic Propulsion Concept Analyses,xe2x80x9d AIAA Journal, Vol. 31, No. 2, pp. 286-293 (Feburary 1993)) have continued to refine the computational methods needed to increase the accuracy of the models.
The performance of the conventional MHD approach is limited, however, in several ways. Phillips assumed a maximum magnetic field of 0.6 Tesla and achieved 8% efficiency. R. A. Doraugh (in xe2x80x9cMagnetohydrodynamic Ship Propulsion Using Superconducting Magnets,xe2x80x9d Transactions of the Society of Naval Architects and Marine Engineering, Vol. 71, pp. 370-386 (1963)) predicted an increase in efficiency to as high as 60% using a 10 Tesla magnetic field and a speed of 10 knots. In order to maintain high thrust, however, such systems use a thrust increase mechanism, which increases the DC current. This, in turn, increases the amount of power wasted in the form of heat (i.e., through I2R), and, as a result, the highest theoretical efficiencies can never be achieved. Furthermore, these systems use high static magnetic fields, which require the use of cryogenically cooled superconducting coils, with all their attendant logistical and maintenance costs, as the Yamato-I experienced while using magnetic fields on the order of only 4 Tesla.
Thus, conventional marine propulsion systems, both mechanical and MHD, are all limited. Clearly, a need exists for a marine propulsion system which (i) is not limited by cavitation, (ii) has a high stored energy to kinetic energy conversion efficiency, (iii) has a small number of moving parts, and (iv) is inexpensive to maintain.
In accordance with the present invention, a method and a system of propelling water are described. The method for propelling water includes generating a water plasma, generating a magnetohydrodynamic (xe2x80x9cMHDxe2x80x9d) momentum in the water using th e water plasma, and propelling the water using the MD momentum. Preferably, the MHD momentum is generated by subjecting the water plasma to a high alternating magnetic field. Preferably, the MHD momentum is generated using induction MHD pumping.
The met hod preferably generates an explosive momentum in the water, which is also used to propel the water. The explosive momentum is preferably generated by a metal-water reaction, and the reaction is preferably generated using a high alternating magnetic field. The high alternating magnetic field is preferably generated by amplifying a conventional alternating magnetic field. In the metal-water reaction, the water reacts with bare liquid metal particles in the presence of high energy. The high energy may come from heat and/or arcing between the metal particles (xe2x80x9cparts-to-particle arcingxe2x80x9d). The arcing may be caused by subjecting the metal particles to the high alternating magnetic field. The bare liquid metal particles are formed by adding heat to solid metal particles in the presence of particle-to-particle arcing. When cold, the metal particles are coated with oxide. The arcing breaks down the oxide coating and allows the heat generated inside the particles to catalyze the metal-water reaction. The heat is generated as a result of eddy currents flowing inside the solid metal particles. These eddy currents are, in turn, induced by the high alternating magnetic field.
In a preferred embodiment, the number of energy conversions is reduced when the water plasma is generated by the metal-water reaction. In this way, the water plasma is generated using high current pulse discharges in conjunction with the reaction.
The method preferably uses sea water, but may also use fresh water. The method may be used to propel a marine vessel or to pump the water, for instance to circulate the water in a cooling system.
The system for propelling water includes a metal fuel, a water plasma, and a high alternating magnetic field that acts on the metal fuel to generate explosive momentum and that acts on the water plasma to generate MHD momentum, and the explosive and MHD momenta propel the water. Preferably, the water plasma is generated by the high alternating magnetic field acting on the metal fuel. Preferably, the MHD momentum is generated using induction pumping. The metal fuel preferably comprises a slurry made of metal particles and the water. The metal particles can be made of aluminum, titanium, copper, or nickel. The high alternating magnetic field can be generated using a magnetic step-up transformer that amplifies a conventional magnetic field.
The present invention provides various technical advantages. One technical advantage is that it provides a marine propulsion system which minimizes the number of moving parts. Another technical advantage is its minimization of the use of energy, which is accomplished in a number of ways. First, wasted heat energy is minimized by reducing the resistance (R) of the sea water through the in-situ creation of water plasma. Second, the marine propulsion system efficiently converts stored energy into kinetic energy without using conventional water-screw technology. Third, the invention takes advantage of efficient induction MHD pumping. Fourth, the invention reuses energy produced in other steps. For example, the water plasma used in MHD pumping is generated by the metal-water explosion; some of the heat used to trigger the metal-water explosion comes from particle-to-particle arcing which also serves to break down the oxide coatings on the metal particles; and eddy currents induced by the high alternating magnetic field create heat to melt the metal particles while still in their oxide coatings, and also are used to trigger the metal-water explosion. The synergy of the various processes minimizes the number of energy conversions and maximizes the simplicity of the system. The benefits of the present invention are (a) compactness, because the propulsion system is self-sustaining and includes a moderate radio frequency electrical power source (which could be replenishable through the metal-water reaction""s excess energy), metal fuel, and an alternating magnetic field amplifier, in a suitable sea water channel; (b) higher energy conversion efficiencies than can be attained by practical superconducting MHD thrusters; and (c) MHD operation without electrodes and their associated electrolytic damage.